JP2000260922A - Method of manufacturing lead frame for semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce warpage and undulation of a lead frame by using a thermoplastic adhesive as an adhesive used for forming a multilayer structure. SOLUTION: The side of a heat spreader 3 of the completed product of a lead frame 10 with a heat sink is set onto a heating plate 8 for reducing warpage and is heated, so that the entire lead frame 1 becomes flat at a temperature at which a thermoplastic adhesive becomes soft. Then, when the lead frame 1 becomes flat by heating, heating is stopped, the lead frame 1 is moved onto a cooling plate 9 for reducing warpage from the heating plate 8 for reducing the warpage, thus cooling the side of the heat spreader 3. A heat treatment is conducted so that the amount of thermal expansion of each member becomes equal at junction temperature where the adhesive becomes hard.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a lead frame for a semiconductor device having a multilayer structure, and more particularly to a method suitable for reducing warpage and undulation of a lead frame with a heat sink.

[0002]

2. Description of the Related Art In general, when manufacturing a lead frame for a semiconductor device having a multilayer structure, a power supply layer or a ground layer (hereinafter simply referred to as a power supply layer) is laminated and joined to a lead frame as a signal layer, or heat is radiated to the signal layer. A structure such as stacking and joining boards is adopted. An insulating material such as a polyimide film coated with an adhesive on both sides is used for joining the signal layer and the power supply layer or the signal layer and the heat sink.

FIG. 3 shows an example of a lead frame with a heat sink. The components are a lead frame 1 as a signal layer, a heat spreader 3 as a heat sink, and a film 2 with a double-sided adhesive for joining the lead frame 1 and the heat spreader 3. The assembly of the lead frame 10 with the heat sink is usually completed by attaching the film 2 with the double-sided adhesive to the lead frame 1 and then attaching the heat spreader 3 (a to
d).

[0004] As shown in FIG. 4, an adhesive 2 a applied to both surfaces of a film 2 is applied to a wire bonding portion 1 a of a lead frame 1 connected to an element 4 and a bonding wire 5.
Is required so that the adhesive is not softened at a high wire bonding temperature of 200 to 250 ° C. Conventional adhesives satisfying such requirements include thermosetting and thermoplastic.

[0005] Many thermosetting adhesives have an adhesive temperature of 200 ° C or lower, and are heated to 200 to 250 ° C during the subsequent curing treatment. On the other hand, a thermoplastic adhesive is an adhesive that does not require a curing treatment, but the bonding temperature is often higher than that of a thermosetting adhesive, and is usually 300 ° C. or higher.

When these adhesives are used, it is necessary to heat these layers or the members constituting the heat sink when the signal layer and the power supply layer or the signal layer and the heat sink are joined. FIG. 2 shows an example of a bonding process of a lead frame with a radiator plate that requires this heating. The film 2 with the double-sided adhesive is attached to the lead frame 1 and set on the heating plate 6 for attachment, the heat spreader 3 is placed thereon, sandwiched between the heating punch 7, and each member is heated (( a), (b)). Each member is thermally expanded when heated and joined when the bonding temperature is reached. Up to this point, since each member is not restrained, even materials having different expansion coefficients and shapes are in a flat state without warpage or undulation.

[0007] When the heating punch 7 is separated to stop heating, the heating punch 7 begins to shrink as the temperature drops, but this time, both are restrained at the joint, and as a result, a difference in the shrinkage amount of each member causes the lead frame to shrink. A finished product in which warpage or undulation occurs is produced ((c), (d)). The amount of warpage or undulation increases as the temperature at the time of joining increases (c, d).

Usually, the warpage of the lead frame needs to be 0.5 mm or less due to a semiconductor assembling apparatus. Therefore, a conventional multi-layered lead frame often uses a thermosetting adhesive having a low joining temperature in order to reduce the amount of warpage or undulation.

[0009]

As described above, a thermosetting adhesive has been used for a conventional multi-layered lead frame. However, this adhesive generates a gas during the curing process and causes the Ag plating of the lead frame. There is a problem that wire bonding failure occurs because it is adsorbed on the surface and contaminates it.

[0010] Therefore, a lead frame cleaning step is required, and there has been a problem that the manufacturing cost is increased.
Also, the adhesive must be stored at a low temperature in a refrigerator or the like in order to prevent the curing from proceeding, and there is a problem that handling is inconvenient.

For these reasons, it is desired to apply a thermoplastic adhesive which does not require a curing treatment or a cleaning treatment to a lead frame having a multilayer structure. Since the thermoplastic adhesive does not require a curing treatment, there is no fear of lead frame contamination, and it is more advantageous than the thermosetting adhesive in terms of manufacturing cost. In addition, since it is thermoplastic, it does not harden even when left to stand, which is convenient in terms of storage.

However, since the thermoplastic adhesive has a high bonding temperature and usually has a temperature of 300 ° C. or more, there is a problem that the warpage or undulation of the lead frame is very large. It is difficult to reduce the value to a specified value (0.5 mm) or less.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to greatly reduce warpage and swell while using a thermoplastic adhesive having characteristics superior to thermosetting properties. Another object of the present invention is to provide a method for manufacturing a lead frame for a semiconductor device.

[0014]

A method of manufacturing a lead frame for a semiconductor device according to the present invention is directed to a lead frame for a semiconductor device having a multilayer structure in which laminated members such as heat sinks having different expansion coefficients are adhered to a lead frame by an adhesive. In the manufacturing method, a thermoplastic adhesive is used as the adhesive, the thermoplastic adhesive is plasticized at the joining temperature, and the laminated member is attached to the lead frame. The lead frame deformed due to the difference in heat shrinkage with the laminated member is flattened, and then cooled to adjust the amount of thermal expansion of the lead frame and the laminated member at the joining temperature of the thermoplastic adhesive equally. is there.

In this case, it is preferable that the heat treatment after the attachment is performed by heating the laminated member, or that the cooling treatment is performed by cooling the laminated member.

Further, the heating temperature of the laminated member is preferably higher than the temperature at which the thermoplastic adhesive softens, and the cooling temperature is preferably lower than the softening temperature. It is preferable that the heating is performed until the entire laminated member is flattened, and the cooling time is performed until the temperature of the entire laminated member becomes equal to or lower than the temperature at which the thermoplastic adhesive softens. This is because, if the processing conditions are not satisfied, the warpage and undulation cannot be flattened. As specific preferable conditions, the heating temperature of the laminated member is 200 to 400 ° C. at which the thermoplastic adhesive softens,
The heating time is 1 to 2 minutes, the cooling temperature of the laminated member is 0 to 40 ° C, and the cooling time is 10 to 60 seconds.

[0017]

[Function] A thermoplastic adhesive has a high bonding temperature and is usually 300.
° C or more, when the laminate is attached to the lead frame using this thermoplastic adhesive, the difference in the amount of heat shrinkage between the lead frame and the laminate due to a subsequent temperature drop causes the lead frame to warp or undulate. Becomes very large.

Therefore, after pasting, a heat treatment is again performed at a temperature at which the thermoplastic adhesive softens to flatten the warpage and undulation of the lead frame. At this time, the flattening is performed because the members softened by the adhesive are released because the adhesive is softened. It is then cooled at a temperature below the temperature at which the thermoplastic adhesive softens. In this cooling process, it is important that a member having a large coefficient of thermal expansion (referred to as Y1) be cooled faster than other members. When a member having a small coefficient of thermal expansion (referred to as Y2) reaches a temperature at which the adhesive cures (assumed to be t2 ° C.), Y1 needs to be at a lower temperature (assumed to be t1 ° C.). It is. At this time, the temperature at which the amount of thermal expansion of Y1 at t1 equals the amount of thermal expansion of Y2 at t2 is t1. As it cools further, Y1 and Y
Since the contraction amount of the lead frame 2 is the same, warping and undulation of the lead frame due to thermal distortion after cooling is eliminated.

As described above, even if a thermoplastic adhesive is used as the adhesive, warping or undulation of the multilayer lead frame can be greatly reduced by subjecting the lead frame to heating and cooling. Therefore, as in the case of using a thermosetting adhesive, the gas generated during the curing process contaminates the lead frame, causing wire bonding failure, requiring a lead frame cleaning step, and increasing the manufacturing cost. You will not have to. In addition, it is not necessary to store the adhesive at a low temperature in a refrigerator or the like, and the handling of the adhesive becomes convenient.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. The process of assembling a lead frame with a heat sink using a film with a double-sided adhesive is the same as the conventional method shown in FIG. In this embodiment, a thermoplastic adhesive having a higher bonding temperature than the thermosetting adhesive is used as the adhesive. As a result, in the finished bonded product, a large warpage or undulation occurs in the lead frame. However, as shown in FIG. 1, the warpage or undulation of the lead frame is reduced by a multilayer lead frame warpage reduction step.

First, the heat spreader 3 side of the finished product of the lead frame 10 with a heat sink is heated by a heating plate 8 for reducing warpage.
The lead frame 1 is set on the upper side and heat-treated until the entire lead frame 1 becomes flat ((a) to (c)). The heating temperature at this time is a temperature at which the thermoplastic adhesive softens, and is usually 200 to 400.
C. and the heating time is 1-2 min.

Next, when the lead frame 1 is flattened by heating, the heating is stopped, and the heat spreader 3 is cooled by immediately moving from the warp reducing heating plate 8 onto the warp reducing cooling plate 9. The cooling temperature at this time is usually about 0 to 40 ° C., and the cooling time is 10 to 60 sec. This cooling treatment is performed in order to equalize the thermal expansion of each member at the joining temperature at which the adhesive becomes hard, and thereby it is possible to reduce the warpage and undulation of the lead frame generated for the above-mentioned reason ((d )-(E)).

Here, a specific warp reduction effect will be described.
When the lead frame material is 42Ni-Fe alloy, the heat spreader material is oxygen-free copper, and the thermoplastic adhesive is an adhesive composed of polyetheramideimide, for example, HM-1 (trade name) manufactured by Hitachi Chemical Co., Ltd. Since the expansion coefficient of the lead frame is greatly different, warping of the lead frame is caused by 3 mm or more when normal assembly is performed.
Cooling treatment is performed at room temperature of 20 to 30 ° C. for 60 seconds.
When sec is performed, the warpage of the lead frame can be reduced to a specified value of 0.5 mm or less.

In the case of a thermoplastic adhesive, it is sufficient that heating for the warpage reduction treatment is 1-2 minutes, and cooling is 10 to 60 seconds, which is 3 minutes in both steps. In the case of a thermosetting adhesive, it takes 2 to 20 hours to perform only the curing process, and furthermore, it is necessary to perform lead frame cleaning, so that the thermoplastic adhesive is simpler in process and has a lower manufacturing cost. Can be lowered.

In the above embodiment, the case where a film with a double-sided adhesive is used for joining the lead frame and the heat spreader is described.
A thermoplastic substance which flows when heated may be used. For example, a thermoplastic adhesive alone formed into a film may be used. Further, the member to be laminated on the lead frame is not limited to the heat spreader, and may be the power supply layer or the ground layer described above, and is not limited to two layers but may be applied to three or more layers.

In the above embodiment, the heating and cooling are performed from the lower side by setting the heat spreader on the plate, but may be performed from the side or the upper side. In the above-described embodiment, a heating plate is used for the heat treatment method. However, other heating methods such as a heater, hot air, and high-frequency heating can be used. In the cooling method, a metal plate such as aluminum, a ceramic plate, or the like can be used for the cooling plate, and a commonly used cooling method such as air cooling can be used as a cooling method other than the plate. The cooling temperature may be other than 0 to 40 ° C as long as it is lower than the heating temperature.

In the above embodiment, if a device such as a plate for heating / cooling treatment is incorporated in an assembling device for a multilayer lead frame, a multilayer lead having no warpage using a thermoplastic adhesive is used. Frames can be produced in large quantities.

[0028]

(1) According to the method for manufacturing a lead frame for a semiconductor device according to the first aspect, a simple process of performing a heating process and a cooling process for planarization while using a thermoplastic adhesive. Thus, warpage or undulation can be effectively reduced, and the manufacturing cost can be reduced as compared with the case where a thermosetting adhesive is used.

(2) According to the method of manufacturing a lead frame for a semiconductor device according to the second aspect, the heat treatment is performed from a laminated member having a simpler shape and structure than the lead frame and having better heat conductivity. Therefore, the processing operation is easy.

(3) According to the method of manufacturing a lead frame for a semiconductor device according to the third aspect, the cooling process is performed from a laminated member having a simpler shape and structure than the lead frame and having better heat conductivity. Therefore, the processing operation is easy.

(4) According to the method of manufacturing a lead frame for a semiconductor device according to the fourth aspect, since heating and cooling are performed under predetermined conditions, compared with the case where a thermosetting adhesive is used. Thus, warpage and undulation can be significantly reduced, and the members can be joined in a short time.

[Brief description of the drawings]

FIG. 1 is a view showing a process of reducing warpage of a lead frame according to an embodiment of a method of manufacturing a lead frame for a semiconductor device of the present invention.

FIG. 2 is a process diagram of attaching a heat sink to a conventional lead frame for a semiconductor device.

FIG. 3 is a manufacturing process diagram of a conventional lead frame for a semiconductor device.

FIG. 4 is a sectional structural view of a conventional lead frame.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lead frame 2 Film with double-sided adhesive 3 Heat spreader (heat radiating plate) 8 Heating plate for reducing warping 9 Cooling plate for reducing warping 10 Lead frame with heat radiating plate

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Takumi Sato 3550 Kida Yomachi, Tsuchiura City, Ibaraki Prefecture Within Hitachi Cable System Materials Laboratory (72) Inventor Shigeo Hagiya 3550 Kida Yomachi, Tsuchiura City, Ibaraki Prefecture Hitachi Cable, Ltd. (72) Inventor Shigeharu Takahagi 3550 Kida Yomachi, Tsuchiura City, Ibaraki Prefecture Hitachi Cable, Ltd.

Claims (4)

[Claims] 1. A method of manufacturing a lead frame for a semiconductor device having a multilayer structure in which a laminated member such as a heat radiating plate to be laminated on the lead frame is adhered to the lead frame by using an adhesive. The laminated member is attached to the lead frame, and after the attachment, heat treatment is again performed to flatten the lead frame deformed due to the difference in the amount of heat shrinkage between the lead frame and the laminated member, and then cooled to join the thermoplastic adhesive. A method for manufacturing a lead frame for a semiconductor device, wherein a thermal expansion amount of a lead frame and a laminated member at a temperature are made equal. 2. The method of manufacturing a lead frame for a semiconductor device according to claim 1, wherein the heat treatment after the bonding is performed by heating the laminated member. 3. The method of manufacturing a lead frame for a semiconductor device according to claim 1, wherein the cooling process is performed by cooling the laminated member. 4. The heating temperature of the laminated member is 200 to 400 ° C. at which the thermoplastic adhesive is softened, the heating time is 1 to 2 min, the cooling temperature of the laminated member is 0 to 40 ° C., and the cooling time is 10 to 10 minutes. 4. The method of manufacturing a lead frame for a semiconductor device according to claim 1, wherein the time is 60 seconds.